A heat pipe can conduct heat from a heat source such as from an electronic device through vapor heat transfer. Typically, the heat pipe includes a working fluid, an evaporator section, and a condenser section. The working fluid is vaporized at the evaporator section. The vapor is received at the condenser section, whereupon the vapor is condensed to form a liquid working fluid. Capillary action and/or gravity returns the condensed working fluid to the evaporator section, thereby completing a cycle.
In many applications, heat pipes of various shapes and sizes are clamped to other elements (e.g., a device or structure generating heat to be removed by the heat pipes) in order to increase the efficiency of heat transfer to and/or from the heat pipes. For example, a plurality of heat pipes can be used in a switching unit for a motor drive. Motor drives are power conversion systems that provide power to electric motors in a controlled fashion. In a switching unit for a motor drive, semiconductor switching devices can be positioned between heat pipes, abutting the evaporator sections of the heat pipes. The assembly of switching devices and heat pipes is clamped together to maintain good electrical and thermal conduction therebetween. Other examples of heat pipe clamping applications and clamping devices exist.
Despite the advantages of clamping heat pipes to other structures as described above, in many cases the preferred clamping forces can damage some heat pipes, such as heat pipes comprising material, dimensions, and/or shapes that make the heat pipes less resistant to deformation under high clamping loads. With reference to switching units as described above, clamping forces can be as high as 20 kN.
As an example of a heat pipe feature that renders the heat pipe less able to withstand desired clamping forces without immediate deformation or deformation (i.e., “creep”) over a period of time, some heat pipes are made of annealed copper, which can be relatively soft. The copper can be annealed for a variety of reasons, such as by being exposed to high temperatures needed to sinter wick material on inside surfaces of the heat pipe. In any case, high desired clamping forces may distort and potentially damage such heat pipes. A distorted heat pipe may degrade heat transfer from the semiconductor devices, and may even damage the devices.
Thus, there has developed a need for a heat transfer device more capable of resisting clamp loads exerted on one or more surfaces of the device, as well as heat transfer and heat clamping systems in which such heat transfer devices are used.